1. Technical Field
The present invention relates generally to telephonic communications, and more particularly to terminal interface circuitry.
2. Background Art
On Sep. 8, 2011 and into the morning of September 9, an electric power failure affected the lives of approximately five million people across southwestern Arizona, San Diego and adjacent areas in California, and northwestern Mexico. The cities of San Diego and Tijuana bore the brunt of this disaster, which started slightly before 4 p.m. PDT and the beginning of a Thursday evening commuter rush hour.
In San Diego, Calif. 13 police stations were left without power but were able to continue operating and taking 911 calls by using generators. In southern Orange County, Calif., the sheriffs department dispatched deputies to busy intersections because traffic lights were out. Essentially all of the traffic lights in Tijuana, Mexico were also out. As evening progressed street lights in San Diego and Tijuana stayed dark and gas stations were unable to pump gas. In Tijuana, power was cut to hospitals and government offices. In the affected areas of Arizona and California, hospitals operating their own power sources generally faired well, even with having to handle increased patient loads due to auto accidents and heat related medical emergencies (temperatures were un seasonal, with highs in much of the affected area ranging from 100° F. to 118° F.).
Of particular relevance here, as MSNBC euphemistically reported, “mobile phone networks were spotty.” In the days following September 8th users of Professor Piggington's Econo-Almanac blog reported their own observations:                TMobile voice and data worked in most [but not all] areas.        I use TMobile and it barely worked. I would be able to dial out and then it would quit.        Cell coverage (Verizon) was less than wonderful in the late afternoon. I assume because everyone was calling everyone else to say they were stuck in traffic . . . . Cell coverage was fine in the evening.        ATT worked on our i-Pad, but very slow. Went down a couple of times, then worked again.        AT&T service on unlocked non-smart phone worked until about 5:45 p.m. yesterday, then displayed “No Network Coverage” until this morning.        
One blog commenter, signing as “CE,” summed up this event as a learning experience (misspelling in the original):                So there are a couple of things that are good to know.        One.        Land Line systems have thier own power supply. The system is on a large battery bank and the generators are required, by FCC mandate, to have several days worth of fuel to support.        Two.        Most cell sites, now, have six hours of battery back up but sometime this won't go six hours due to extremly large loads at the cell.        Three.        Here is the stupid part. Some cell sites have fiber to them instead of T1s. While the FCC mandated that the cell sites has 6 hours of battery back up the fiber converter that translate DS0s only has two hours. So the site could keep going except its backhaul has dropped off. Mean while . . . . Like I said earlier cell sites that are connected via T1s should remain up for the duration of the cell sites batteries.        Four.        VoIP systems will fail because you do not have a local power supply. IDCs will have power, the same way that local land line switchs do, and the connection is still there but the local reciever (modem) will not have power . . . .        
The above event was not unique, even in North America. For example, in 2008 a blackout in southern Florida affected 4.5 million customers for hours. The biggest blackout in the U.S. occurred on Aug. 14, 2003, disrupting power in eight U.S. states and Ontario, Canada. Over 55 million people were affected, with service in major cities, such as New York and Toronto, not fully restored for two days.
One thing that has changed since 2003 and even 2008, however, is the increasing usage of mobile telephones and the degree of reliance that out society places on these. The 2003, 2008, and 2011 events serve to illustrate that we have an existing and growing problem in our telecommunications infrastructure.
[In the following, reference numbers are used to denote generic or collective elements, and reference numbers with letter suffixes are used to denote specific elements or types of elements. For example, telephones 12, generic, versus a POTS telephone 12a and cell phones 12d, specific.]
FIGS. 1a-b (background art and prior art, respectively) depict a very basic telecommunications network 10, wherein FIG. 1a is a block diagram showing network elements and FIG. 1b is a stylized depiction of these network elements in use. The telecommunications network 10 here comprises two telephones 12a-b connected by a communications channel 14.
FIG. 2 (background art) depicts a slightly more sophisticated but still rather basic telecommunications network 10. Here two telephones 12a-b are connected to respective subscriber sub-channels 16a-b, that in turn connect to respective aggregation nodes 18a-b, which are connected by an inter-provider sub-channel 20.
Many labels in telecommunications have become obsolete. For example, subscriber sub-channels 16 have often been termed “local loops,” “landlines,” and the “last mile,” due to the historic use of analog signals in copper wire pairs in pole supported cables connected to necessarily nearby aggregation nodes 18. Today these labels are too limiting (e.g., for cellular telephone service). Similarly, aggregation nodes 18 have often been termed “central offices” or “switches,” due to the historic use of switches located at telephone service provider offices. Today these labels are also too limiting (e.g., field-located digital loop carrier (DLC) units and serving area interfaces (SAI)). Also similarly, inter-provider sub-channels 20 have often been termed “trunk lines,” due to the historic use of multi-conductor cables or lines. Today that label as well is too limiting (e.g., satellite links). In general, the use of historic but obsolete labels is avoided herein.
In telecommunications today, hundreds of millions of telephones 12 and their respective subscriber sub-channels 16 are serviced by hundreds of thousands of aggregation nodes 18, that in turn are connectable with tens of thousands of inter-provider sub-channels 20. At the end of 2009 there were nearly 6 billion mobile and fixed-line subscribers worldwide, comprising 1.26 billion fixed-line subscribers and 4.6 billion mobile subscribers. (John, Richard R., Network Nation: Inventing American Telecommunications, Harvard University Press, 2010).
FIG. 3 (background art) depicts three representative communications examples in a modern telecommunications network 10. In the first example, telephones 12a-b are connectable via a first communications channel 14a. For the sake of this discussion let us say that we have a real estate broker in a small office in rural North America who is calling her home a few blocks away, to leave a message for her children.
The telephones 12a-b here are respectively connected via subscriber sub-channels 16a-b to a single aggregation node 18a. The office telephone 12 here is a plain old telephone service (POTS) type device (POTS telephone 12a), and it is especially notable here for two reasons. First, subscriber-side POTS telephones 12a are provider-side powered (e.g., from the aggregation node 18a here). Second, signals between a POTS telephone 12a and an aggregation node 18a are analog.
In contrast, home telephone 12 here is a common cordless telephone 12b having a base station portion and a hand set portion that intercommunicate using radio frequency signals. The base station portion is powered from a small plug-in transformer, that in turn is powered with building mains power from a wall outlet. The hand set portion is portable and is powered from an internal battery, which is recharged when the hand set portion is placed in the base station portion. The radio frequency signals used may be analog or digital. Nonetheless, it is analog signals that are used between the cordless telephone 12b and at least part of the way to the aggregation node 18a. 
[Telephone service via coaxial and fiber optic cables are special cases where analog-digital conversion is made, usually where the service enters the premises, and the signals onward to the aggregation node are digital. Service such as this is increasingly common where households have combined cable TV, Internet, and telephone combination service. However, such telephone service is not particularly germane here.]
Continuing, the subscriber sub-channels 16a-b here are both traditional copper wire pairs connected to the local aggregation node 18a. 
In the second example in FIG. 3, telephones 12a, 12c are connected via a second communications channel 14b. Continuing with our hypothetical real estate broker, let us now say that she calls the hotel room of clients who are vacationing in Europe, to inform them that an offer they made on a property has been accepted. Proceeding from left to right, the office POTS telephone 12a connects via the subscriber sub-channel 16a to the local aggregation node 18a; the aggregation node 18a connects via inter-provider sub-channel 20a to the aggregation node 18b; the aggregation node 18b connects via inter-provider sub-channel 20b to the aggregation node 18c; the aggregation node 18c connects via inter-provider sub-channel 20c to the aggregation node 18d; the aggregation node 18d connects via inter-provider sub-channel 20d to the aggregation node 18e; and the aggregation node 18e connects via subscriber sub-channel 16c to the hotel room telephone 12 here, which is a Voice over Internet Protocol device (VoIP telephone 12c).
The POTS telephone 12a, subscriber sub-channel 16a, and aggregation node 18a have already been discussed, and the elements between aggregation node 18a and aggregation node 18e are not particularly germane here. The VoIP telephone 12c here is notable for two reasons. First, VoIP telephones 12c are subscriber-side powered, usually from a local interface device like a router that receives building power. Second, signals between VoIP telephones 12c and aggregation nodes 18e are entirely digital.
In the third example in FIG. 3, telephones 12c, 12d are connected via a third communications channel 14c. Continuing now with our hypothetical European vacationers, let us say that the husband receives the real estate agent's call but that his wife is away from the hotel shopping. He therefore uses the hotel room's VoIP telephone 12c to call her cell phone 12d to inform her of the offer acceptance. The VoIP telephone 12c accordingly connects via the subscriber sub-channel 16c to the local aggregation node 18e; the aggregation node 18e connects via inter-provider sub-channel 20e to aggregation node 18f; and the aggregation node 18f connects via subscriber sub-channel 16d to the cell phone 12d. 
The VoIP telephone 12c, subscriber sub-channel 16c, and aggregation node 18e have already been discussed, and the inter-provider sub-channel 20e here is also not particularly germane. The cell phone 12d here is battery powered, with the battery being rechargeable via a universal serial bus (USB) port in the cell phone 12d. Intercommunication here over the subscriber sub-channel 16d is via radio waves.
FIG. 4 (background art) is a simplified version of FIG. 3, with some pertinent information added and some minor changes made to facilitate discussion. For present purposes, everything between the aggregation nodes 18 here is presented as generic inter-provider sub-channels 20 connecting with a central cloud 24. FIG. 4 depicts the cellular aspects of the telecommunications network 10 slightly different than in FIG. 3. Here everybody has a cell phone 12d and there are ubiquitous sets of cellular aggregation nodes 18f. Also, for completeness and later discussion a generic power source 26 is depicted.
FIG. 4 serves now to discuss some generalizations about the history of telephony. Today we have, plain old telephone service (POTS), public switched telephone network (PSTN) service, and cellular service all coexisting and in wide use. The POTS telephone 12a, the cordless telephone 12b, and the subscriber sub-channels 16a-b here employ what is widely termed “POTS technology.” The VoIP telephone 12c, the subscriber sub-channel 16c, and the aggregation node 18e employ digital Internet Protocol (IP) technology. The cell phones 12d, the subscriber sub-channel 16d, and the aggregation nodes 18f employ radio based digital “cellular technology.” Additionally, the aggregation nodes 18b-f, the inter-provider sub-channels 20, and the cloud 24 employ digital “PSTN technology” or Internet Protocol (IP) technology, with the aggregation nodes 18 typically interfacing between respective technologies as needed.
Generalizing, POTS technology is analog and PSTN technology is digital. Starting in the early 1960's, analog POTS in the telecommunications network 10 started to be converted over to digital PSTN, and digital IP and cellular technologies subsequently followed. The process of analog to digital equipment conversion is near complete, except for some telephones 12 and subscriber sub-channels 16. In the interest of backwards compatibility, many local aggregation nodes 18 still can handle analog POTS communications. POTS and PSTN services were historically subject to different political considerations than the newer cellular and VoIP services. POTS grew during the early years of the cold war, PSTN grew during the later years of the cold war, and cellular and VoIP have grown in the post cold war era.
POTS and PSTN were viewed as critical national infrastructure. Few today remember when POTS was the only service available. In contrast, many today appreciate that the Internet was developed adjacent with and melded with PSTN. The widely accepted notion that the Internet was designed to survive a nuclear attack serves to emphasize just how robust most POTS and PSTN services were and continue to be designed. Also, POTS and PSTN largely necessitated monopolies for their efficient operation, and governments therefore dictated many aspects of design and strongly regulated the major market participants.
In contrast, cellular and VoIP technologies have grown largely as parallel options to POTS and PSTN in most places, and these technologies do not necessitate monopolies. Governments have therefore not generally had the justification or motivation to dictate design or regulate market participants.
Turning now particularly to cellular technology, the overwhelming considerations for it have been lowest pricing and newest features. Today cell phones 12d are often given away to subscribers in exchange for 1-2 year service contracts and the life cycle of a cell phone, from design through to obsolescence, can be as little as two years.
Over the shorter history of cellular service, some aspects of cell phones 12d have and continue to become standardized. For example, the rightmost cell phone 12d in FIG. 3 was described above as being a “smart phone,” with a USB port that doubles as a power connection port. This power arrangement has become largely standard for all new cell phones 12d today. Similarly, many new cell phones 12d use hardware (e.g., digital signal processors) and software (e.g., the Android™ operating system) that permit very flexible yet powerful software applications. For instance, a Motorola Droid™ device inherently has radio frequency coverage for cellular bands, Wi-Fi, and Bluetooh™, but can be programmed to handle essentially any protocol that uses the same or close radio frequencies. Moreover, while cellular telephone programming historically has required considerable specialized talent and entailed substantial learning of the target device, the emerging use of standard operating systems (e.g., Google's Android™ OS) increasingly permits those with barely any programming talent to create their own software applications in a few hours.
The overwhelming consideration for VoIP service has been very low cost of operation. Aside from an initial equipment investment, VoIP is almost free and its cost is not tied to the amount of usage. Today VoIP telephones 12c are increasingly common in business environments, because most business have Internet connectivity and are motivated to minimize operating costs. Nonetheless, some recently variations of VoIP have become popular with travelers and in home environments. Probably the two most well known of these are Skype™ and MagicJack™.
Skype™ is a software application that allows users to make voice and video calls and chat over the Internet. Calls to other users within the service are free, while calls to traditional POTS/PSTN telephones and cell phones can be made for a fee. Many subscribers are business travelers who use laptop or tablet computers to make economical long distance calls. If a computer or computerized device has a microphone and a speaker it can likely be used. Alternately, handsets or head sets that plug into a USB port of a computer or computerized device can be bought for use with the service.
MagicJack is a device that plugs into a USB port on a user's computer and that has a standard RJ-11 phone jack into which any standard POTS/PSTN telephone can be plugged. The User's computer must have Internet access, but then is able to make calls to almost any phone in the U.S. and Canada.
Changing tact now, let us consider how the telecommunications network 10 in FIG. 4 can fail. Failures can generally be classified as equipment breakdown, equipment overload, and underlying infrastructure failure.
Equipment breakdown is straightforward. One can minimize this by building more robust equipment or one can mitigate this by providing redundancy. In the case of the cloud 24, both approaches are widely employed. The cloud 24 can be spoken of as being a part of, as itself being, or as including the Internet, and it can be recalled here that the Internet was purportedly designed to withstand nuclear attack.
In contrast, telephones 12 vary considerably in their resistance to breakdown. Some are wonders of robustness, whereas others breakdown easily. Many older style POTS telephones 12a are very robust, largely due to their original design having occurred when redundancy was rare and expensive (e.g., a telephone was a substantial investment, often leased from the TelCo on a monthly basis), and one telephone per home was felt sufficient. Business telephones 12 (e.g., VoIP telephone 12c) are typically next in robustness, largely due to businesses being willing and able to pay for increased reliability, and seeking to reduce operating costs. Modern household telephones 12 (e.g., cordless telephone 12b) are usually another matter. These are widely regarded as a cheap commodity and they are typically replaced every 2-3 years, if for no other reason than that consumers want newer features. Portable telephones 12 (e.g., cell phones 12d) are generally the most subject to breakdown. This is due partly to their inherently being subject to a higher level of abuse. Regarded also as a cheap commodity, these are also usually expected to only last 1-2 years, until a replacement is obtained with a new service agreement or until a superseding model with newer features becomes available. In passing here, it should also be noted that cordless telephones 12b and cell phones 12d have batteries that can completely discharge (effectively resulting in a temporary breakdown) or that can literally breakdown. As FIG. 4 indirectly implies, we now have a considerable amount of redundancy in telephones 12 today, particularly due to cell phones 12d becoming essentially ubiquitous in modern society.
Subscriber sub-channels 16 also vary considerably in their resistance to breakdown. Suffice it to say that what can reasonably be done to make these more robust usually is done. As for redundancy, subscribers can pay for multiple lines, but adjacent subscriber sub-channels 16 tend to fail together (e.g., by a commonly used cable being cut).
The resistance to breakdown of local aggregation nodes 18 (e.g., aggregation nodes 18a, 18e, 18f) also varies. A lot of the “survive nuclear attack” design is still found in almost all non-cellular type aggregation nodes 18, and even smaller, local instances are usually robustly built with considerable internal redundancy. In the United States and many other countries, non-cellular aggregation nodes 18 are usually battery powered, with charging systems that have at least one back-up power source. Back-up generators and fuel supplies that will last at least for hours are mandated by government regulations.
Aggregation nodes 18 for cellular service are often markedly different. In a cellular scheme each local node is often part of an overlapping grid. If one breaks down, others may be able to seamlessly cover. Additionally, lulled into a sense of security because POTS and PSTN widely coexist, consumer concern and government involvement is often considerably less here. Notably, where there are government regulations requiring back-up generators, the requirements for fuel supplies are lower than such for non-cellular aggregation nodes 18.
Continuing with how the telecommunications network 10 in FIG. 4 can fail, equipment overload is a rapidly growing but underappreciated possibility. POTS and PSTN services generally have much higher resistances to overload than cellular services. The history of POTS and PSTN as critical communications infrastructure, and close government design and regulatory involvement, have resulted in these having high capacity to subscriber ratios. For instance, if there is a natural or man-made disaster and 10% of POTS or PSTN subscribers concurrently attempt to make calls, most if not all will get a dial tone, be able to enter a telephone number, and be able to call across the street or around the world. In contrast, if there is a similar disaster and 10% of cellular subscribers concurrently attempt to make calls, the cellular services will likely overload or outright crash.
Continuing further with how the telecommunications network 10 in FIG. 4 can fail, we come to underlying infrastructure failure. In general, this means power failure.
The older style POTS telephone 12a fairs best here. It is line powered, meaning that it receives all necessary power for operation from its local aggregation node 18, via copper wires in the subscriber sub-channel 16. The cell phone 12d also tends to fair well when the electric power goes off. It is, however, subject eventually to battery depletion, say from repeated unsuccessful attempts to get through on an overloaded cellular service.
The cordless telephone 12b and the VoIP telephone 12c do not fair at all here, at least not without a backup power source (which is uncommon and in some cases simply will not help anyway). Recall that cordless telephones 12b and the VoIP telephones 12c employ local power sources, such as standard wall power outlets.
Accordingly, in view of our increasing reliance on easily disrupted power sources for localized telephone communications, what is needed is a mechanism to decrease such reliance. In particular, in view of the advantageous power-related features of analog POTS and PSTN technologies and the disadvantageous fact that consumer's digital telephonic-capable devices today cannot utilize such power-related features, such a mechanism should permit consumer's digital telephone devices to interface with provider's analog telephone services.